JAVA学习第四十课（常用对象API）- Map集合练习

一、LinkedHashMap集合

import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;

public class Main
{
	public static void main(String[] args) {
		HashMap<Integer, String> hm = new LinkedHashMap<Integer,String>();//保证有序
		hm.put(1, "a");
		hm.put(5, "c");
		hm.put(3, "e");
		hm.put(4, "s");
		Iterator<Map.Entry<Integer,String>> It = hm.entrySet().iterator();
		while(It.hasNext()){
			Map.Entry<Integer, String> meEntry = It.next();
			Integer key = meEntry.getKey();
			String value = meEntry.getValue();
			System.out.println("key - value :"+key+"-"+value);
		}
	}
}

练习：

记录字母出现次数

import java.util.Iterator;
import java.util.Map;
import java.util.TreeMap;

/*"as6&dg+dfg-badf453sasxa" 记录字符串中字母出现的次数 a(4)b(1) d(4)...
 *
 * 思路：
 * 很容易发现，字母和次数之间存在对应关系，而且需要存储
 * 能存储映射关系的集合有数组和Map
 * 判断关系中的一方是否是有序编号？否
 * 需要使用Map集合
 * 判断具备唯一性的一方具备着顺序如a，b，c。。。
 * 所以使用TreeMap
 * */
public class Main
{
	public static void main(String[] args) {
		/*
		 * 1.将字符串变成单个字母的字符数组
		 * 2.用每个字母当中键去查Map集合的表
		 * 3.判断字母是否存在，不存在按      字母<key> - time<value>的方式存储 （初始time = 1）
		 * 存在，按      字母<key> - ++time<value>的方式存储
		 * */

		String str = "asdgdfgbadfsasxa";
		String result = Get(str);
		System.out.println(result);
	}
	public static String Get(String str){

		char[] ch = str.toCharArray();
		Map<Character,Integer> map = new TreeMap<Character,Integer>();
		for (int i = 0; i < ch.length; i++) {
			if(!('a'<=ch[i]&&ch[i]<='z' || 'A'<=ch[i]&&ch[i]<='Z'))
				continue;
			Integer value =  map.get(ch[i]); //将字母作为键查表
			int time = 1;
			if(value!=null)
				time = value + 1;
			map.put(ch[i], time);
		}
		return Map_To_String(map);
	}
	private static String Map_To_String(Map map)
	{
		StringBuilder str = new StringBuilder();
		Iterator<Character> it = map.keySet().iterator();
		while(it.hasNext()){
			Character key = it.next();
			Integer value = (Integer) map.get(key);
			str.append(key+"("+value+")");
		}
		return str.toString();
	}
}

二、Map集合查表法

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Scanner;
import java.util.TreeMap;
import javax.management.RuntimeErrorException;

public class Main
{
	public static void main(String[] args) {
		/*在查表法中Map集合的应用较多*/
		int num;
		Scanner in = new Scanner(System.in);
		num = in.nextInt();
		String week = Get_Week(num-1);
		System.out.println(week);
		System.out.println(Get_Week_English(week));
		in.close();
	}
	public static String Get_Week(int num){
		if (num>7 || num <0)
			throw new RuntimeException("输入错误");

		String[] week = {"星期一","星期二","星期三","星期四","星期五","星期六","星期天"};
		return week[num];
	}
	public static String Get_Week_English(String week){
		Map<String, String> map = new HashMap<String, String>();
		if(!(week.equals("星期一")||week.equals("星期二")||week.equals("星期三")
				||week.equals("星期四")||week.equals("星期五")||week.equals("星期六")||week.equals("星期天")))
				{
			throw new RuntimeException("输入错误的星期");
				}
		map.put("星期一", "Monday");//特别注意一点，map.put("",Set<Integer>);集合中也可以放集合
		map.put("星期二", "Tus");
		map.put("星期三", "Wes");
		map.put("星期四", "Thu");
		map.put("星期五", "Fri");
		map.put("星期六", "Sta");
		map.put("星期天", "Sun");
		return map.get(week);
	}
}